President Carter yesterday proposed reductions in federal impact aid to schools that would cost Washington-area school systems more than $13 million in the year starting Oct. 1.

The Carter plan immediately was denounced by Washington-area members of Congress. Rep. Herbert E. Harris II (D-Va.), whose Northern Virginia district would be hardest hit, announced a special congressional hearing on the subject next Monday at 7:30 p.m. at Alexandria City Hall.

Carter is the latest in an unbroken line of chief executives to seek reforms, in the impact aid program, which was designed to aid school districts where a heavy concentration of nontaxpaying federal installationa and employes adversely "impacts" on school financing. But it has been the object of much critism because wealthy school districts, most notably several in suburban Washington, are the major benefactors.

The Carter proposal would eliminate from eligibility children of federal employes who work outside the jurisdiction in which their children attend school. An earlier reform eliminated funds for children whose parents cross state lines to work at federal sites.

"I think we can beat it again," said Harris, who announced that Rep. Carl Perkins (D-Ky.), chairman of the House Subcommittee on Elementary, Secondary and Vocational Education, would chair the meeting in Alexandria.

Health, Education and Welfare Secretary Joseph A. Califano Jr., who explained the president's education package to Perkins' committee yesterday, acknowledged in prepared remarks that it has become "an annual rite of spring for the executive branch to march up Capitol Hill with a broad proposal to reform impact aid and to march down the Hill in the summer without it."

During a break in the testimony, Califano said that the Carter administration "clearly has come up with a mederate proposal" that rates a better-than-usual chance of acceptance by Congress.

Califano defended the proposal by saying the affected students "are not associated with a loss of taxable property to the school district because they live on taxable residential property within the district."

To offset a sudden loss of revenue because of the changes, the cuts would be phased in over the next three years. Califano said passage of the program would cut program costs by $76 million, to $735 million, in the fiscal year beginning Oct. 1, and by $336 million in fiscal 1982.

Harris and Rep. Joseph L. Fisher (D-Va.) notified Northern Virginia school superintendents of the proposed changes yesterday and urged them to be among those offering testimony next Monday. Harris said the hearing offers "a unique opportunity for those concerned about quality education to influence legislation."

A member of Harris' staff offered this table of how the proposal would affect area school systems:(TABLE) Jurisdiction(COLUMN)Current Aid(COLUMN)Carter Plan(COLUMN)Loss Alexandria(COLUMN) 1,133,185(COLUMN) 835,733(COLUMN) 297,452 Fairfax County(COLUMN)13,092,286(COLUMN) 8,913,897(COLUMN) 4,178,339 Prince William(COLUMN) 2,374,114(COLUMN) 1,616,418(COLUMN) 757,696 Falls Church(COLUMN) 81,374(COLUMN) 55,404(COLUMN) 25,970 Arlington(COLUMN) 1,749,155(COLUMN) 1,190,914(COLUMN) 558,241 Loundoun(COLUMN) 475,064(COLUMN) 328,342(COLUMN) 164,722 Montgomery(COLUMN) 3,785,652(COLUMN) 2,597,524(COLUMN) 1,188,128 Prince George's(COLUMN) 7,829,918(COLUMN) 5,331,008(COLUMN) 2,498,910 Anne Arundel(COLUMN) 6,764,011(COLUMN) 4,655,543(COLUMN) 2,108,468 District(COLUMN) 5,255,000(COLUMN) 3,903,000(COLUMN) 1,352,000 Total(COLUMN)43,039,759(COLUMN)29,427,783(COLUMN)13,111,976(END TABLE)